Mechanically frothed foams have been limited in density reduction in part due to limitations of current surfactant technology used for mechanically frothed foams. Typically the surfactants used for the mechanically frothed foam processes are polydimethylsiloxane/polyether repeating block or (AB)n-type copolymer. For example, hydrolyzable (AB)n surfactants are disclosed in U.S. Pat. No. 3,947,386 and non-hydrolyzable (AB)n surfactants are disclosed in U.S. Pat. No. 3,957,842, both for use in the mechanical froth foam process. The use of either hydrolyzable or non-hydrolyzable (AB)n surfactants in making foam articles including carpet backing is described U.S. Pat. Nos. 4,022,722 and 4,022,941. Furthermore, processes for making (AB)n surfactants are described in U.S. Pat. Nos. 5,869,727 and 4,150,048.
One attempt to lower foam density is by using chemical blowing from the reaction of water with isocyanate as described in U.S. Pat. Nos. 6,790,872 and 6,372,810, however, these processes are limited in density reduction in part to the physical limitations of the current surfactant technology. These two patents describe the use of a single surfactant in the composition along with water used for the reaction of water with isocyanate to give added blowing and density reduction.
Processes for making CB(AB)nC surfactants using a chain-terminating group, C, (where B is the silicone and A is polyether) to control molecular weight of the nearly (AB)n molecule is disclosed DE 198 36 260.
Mechanically frothed polyurethane foam made with silicone surfactants of a certain composition and molecular weight is disclosed in U.S. Pat. No. 4,483,894 wherein the surfactant is a poly(dimethyl)siloxane/polyalkyleneoxide copolymer with greater than 60% by weight of the polyalkyleneoxide being oxyethylene groups that also represents at least 40% of the weight of the entire copolymer, and with the content of dimethylsiloxane from 15-40% by weight of the copolymer. However, the surfactants used in the disclosed process do not provide for low froth density when compared to surfactants of the (AB)n-type and when used in oven cured conditions have associated foam stabilizing problems which results in higher final foam density.
However, there still remains a need in the art for lower polyurethane foam density in mechanically frothed foams with or without the use of chemical blowing assistance from the water/isocyanate reaction. The instant invention provides a solution to this problem.
It would be desirable, in the art of preparing polyurethane foams, to have a polyurethane foam-forming composition that can be mechanically frothed such that a foam having suitable fine cell structure and good properties, including low compression set, can be prepared. It would also be desirable in the art to have a process for preparing polyurethane foam having good physical properties and low density by use of the mechanical froth process.